This invention relates to an optical disk fabricating method, optical disk, and optical disk apparatus, and more particularly, to the fabrication, recording and reproduction of optical disks that have been formed according to the so-called land/groove technique.
Currently, the DVD (Digital Versatile Disc) is being proposed as an optical disk apparatus for recording information at high density. The DVD is designed to be able to record 2.6 GB of data on a single side, the recording being performed by irradiating a laser beam having a wavelength of 650 nm onto an optical disk through an optical system having a numerical aperture of 0.6. Using this technique, about one hour""s worth of image signals can be recorded on a single side of a disk.
However, a typical home video tape recorder (VTR) has a basic recording time of two hours. Thus, in order for DVD""s to become a viable substitute for VTRs, they must be provided with the capability to store more data. For example, although editing or the like can be performed by effectively using the characteristic functions of optical disk such as random access, about three hours"" worth of image signal must be recorded in order to make DVDs desirable. In the case of a DVD system, a three hour recording time means that the disk should be capable of storing about 8 GB of data.
For this reason, it is necessary to make effective use of the information recording surface of an optical disk.
The present invention has been made with the above points in mind. Accordingly, an object of the invention is to provide an optical disk fabricating method, optical disk, and optical disk apparatus which permit effective use of the information recording surface of the disk, thereby allowing data to be recorded at higher density than before.
A technique for fabricating an optical storage disk according to the invention involves providing a base disk having a transparent layer and a recording layer, the transparent layer having a thickness between 10 xcexcm and 177 xcexcm; and irradiating the base disk with a laser beam so as to form a multiple of recording tracks on the recording layer, the tracks being substantially concentric about the center of the base disk, having a track pitch of 0.64 xcexcm or less, and alternating radially between land tracks and groove tracks, wherein each land track is located on the surface of the recording layer and each groove track is located within a groove on the surface of the recording layer.
When the invention is applied to an apparatus accessing the type of optical disk described above, groove tracks and land tracks are accessed by irradiating the laser beam onto the disk via an optical system having a numerical aperture of 0.78 or more with a working distance being set to 560 xcexcm or less. The rotation speed of the optical disk may be switched in stages from the inner circumferential side to outer circumferential side of the optical disk by noting the irradiation position of the laser beam.
Forming the light transmission layer with a thickness of 10 xcexcm to 177 xcexcm allows an optical system having a high numerical aperture to read data from the disk; and data can be recorded at high density. By spirally forming tracks with a pitch of 0.64 xcexcm or less on the information recording surface, the information recording surface can be effectively used, thereby helping to improve recording density. Recording density may be further improved by ensuring that the width of a groove and that of a land are equal or almost equal.
In the optical disk apparatus of the invention, the recording density advantages of the above-described disk are realized by accessing groove tracks and land tracks. Moreover, by switching the rotation speed of the optical disk in relation to the radial position of the irradiating laser, additional recording density advantages may be realized.